1. Field of the Invention
The present invention relates to an imaging apparatus. It has particular utility in relation to an imaging apparatus operable to obtain an image of one or more facial features of a user.
2. Related Art
One known apparatus of this type forms a component of the IriScan 2000 EAC(trademark) iris recognition apparatus manufactured by lriScan Inc. The apparatus includes an image capture unit comprising a wall-mounted body portion which rotatably supports a tiltable housing containing the optical elements used in the apparatus. The camera and path-bending optics inside the housing are arranged so as to provide the camera with a view through an aperture provided in the front wall of the tiltable housing. The housing additionally contains a liquid crystal display (LCD display) which is viewed by the user during the iris recognition procedure through the same aperture. The LCD display is driven by the video signal which is currently being output by the camera.
In using the apparatus, the user moves his head until the LCD display shows an in-focus image of one of his eyes. Because of safety constraints on the level of illumination of the human eye, the depth of focus of the apparatus is limited and the user must position his head within a relatively narrow range of distances from the apparatus. The magnification of the optical system is arranged such that, when in focus, the image of one eye fills more than one-third of the field of view of the camera. This is useful in assuring that the iris is imaged in sufficient detail to obtain an iris data sequence which is unique to that iris.
The cost of the LCD display in the above apparatus is significant. Although the use of iris recognition technology is clearly desirable because of the high level of security it affords, the current cost of iris recognition units hinders their incorporation into credit card payment terminals and the like.
Other proposed iris recognition apparatuses avoid the requirement that the user moves his head to a preferred position in relation to the apparatus, instead providing a camera with both an auto-focus and an auto-zoom facility. Although this relaxes the constraints imposed on the distance between the user and the apparatus, it does not provide a facility for aligning the eye within the field of view of the camera. Hence, the use of a Pan Tilt Zoom camera in conjunction with eye-tracking techniques has been proposed to ensure that the user""s eye is included within the obtained image. The use of such devices markedly increases the unit production cost of the imaging component of the iris recognition apparatus.
Identification Technologies International Inc. produce a PAC-1000 facial recognition system. The image capture part of the apparatus has a mirror on its front surface in which the user can see his reflection. Although this places constraints on the transverse position of the user""s face, it does not place any positive constraints on the distance between the user and the device. The user is, of course, able to estimate his distance from the apparatus owing to its apparent size (i.e. owing to perspective), but that is not a sufficiently accurate indication to enable him reliably to adopt a preferred position in relation to the apparatus.
Accordingly, the present invention provides a facial feature imaging apparatus comprising:
a camera apparatus operable to capture an image of one or more facial features of a user, light reflected from said facial features travelling along an optical path from said facial features to said camera apparatus;
a visible light reflector disposed on said optical path, and positioned such that, in use, the user can see his reflection therein, said reflector being arranged to present a reflection of the user, which reflection gives a positive visual indication to the user that he is within a preferred range of distances from the camera.
By providing a visible light reflector which is arranged to present a positive visual indication to the user that he or she is within a preferred range of distances from the camera, feedback is provided to the user enabling him to position his head at a correct distance from the apparatus. The visible light reflector provides this feedback as effectively as known devices but more cheaply than has hitherto been possible. The provision of such a visible light reflector reduces the need for a camera with an auto-focus (and possibly auto-zoom) facility. Furthermore, by arranging the reflector to lie on optical path between the user and the camera, the apparatus is made more compact than known apparatuses. The reflection provides a positive indication in the sense that there is some indication other than the user being able to judge his distance from the camera owing to perspective.
Preferably, the reflector comprises one or more optical elements which, in combination, have an optical power greater than zero. This has the result that the reflection seen by the user undergoes changes in both size and orientation as the user approaches the apparatus.
Preferably, the reflector comprises a non-planar reflector, the surface of which is shaped so as to present said positive visual indication. The advantage of such visible light reflectors is that they comprise few components and hence are inexpensive to manufacture.
In preferred embodiments, the mirror presents a concave surface to the user. The concave surface may be spherical or aspherical. Spherical mirrors usually cost less than aspherical ones.
Some embodiments of the present invention use a camera which is responsive to light outside the visible portion of the electromagnetic spectrum. For example, the camera used may responsive to infra-red light, in which case the reflector used can be a wavelength-selective mirror, which reflects visible light but allows the passage of infra-red light, placed in the aperture in the housing. It will be appreciated that this arrangement allows infra-red light reflected from the user""s face to pass through the mirror and continue along an optical path towards the camera.